yes you can .
A good starting point is the video by Maria Gutierrez in the CS SDK Team blog.
I've been using for some time the SDK only in Flash Builder, so I can assure you it's possible to accomplish the task - nevertheless, since I've got Extension Builder, it's *far* easier to code, test and debug.
By the way, this documentation is good for you even if you don't own Extension Builder.
That's exactly the information I was looking for. Including the debugging flag option so I don't have to sign the extension. Just some follow up Though. Is there some nice examples for modifying the Flash IDE? I noticed the CSAW doesn't have a specific library for Flash? I'm assuming the "bridge" covers this. However, not certain as to what functionality might be available to me. I'm hoping to access layers (layer selection events), add documents and read content values from a flash document. Is this possible?
Check out CSXSInterface.evalScript()...